Flexible wave guide for ultra high frequency energy



Feb. 24, 1948. E. c. CORK 2,436,421

FLEXIBLE,WAVE GUIDE FOR ULTRA HIGH FREQUENCY ENERGY Filed May 12, 1943 mum/runs 3mm, m5 POLYETHYLENE I w 9 lei/BEER ERA/0E0 0/150 camsfiW/RE PULYETHVLE/VE INVENTOR. EDWARD CECIL CORK A TTORNEY Patented Feb. 24, 1948 FLEXIBLE WAVE GUIDE FOR ULTRA HIGH FREQUENCY ENERGY Edward Cec l Cork, Ealing, London, England, as-

signor to Electric & Musical'lndustries Limited.

UNITED STATES PATENT "OFFICE losses due to circulating currents. lowing specification and claims what is meant Hayes, Middlesex, England, a company or Great Britain Application May 12, 1943,. Serial No..486,715

.lInGreat' Britain February 3; 1941 Section 1, "Public Law '69(Lt-August'8, 1946 f-latentzexpires January. 30; 1962 I TClaims.

This: invention relatesto the transmission of .electrical energy-by 'electric cables of the concentric line type comprisingan inner conductor held in spaced relationship with-respect to a surrounding tubular conductor,and electric waveguides in the form ofnhollow conductors along which electricwaves-radiated from a source (such area dipole aerial) can be propagated, and to systems embodying such cables and wave guides.

'Theouter tubular conductor of a concentric cable-sometimes comprises a lead sheath, but such acabl'e is not found to besatisfactory where flexibility is desired, since although a certain degree of flexibility is inherent in the cable, nevertheless, if the cable is bent the tubular conductor not infrequently .becomes distorted with the result that the characteristic of the cable is impaired to such an extent as to render the cable unsuitable for use at ultra high frequencies corresponding to centimetre wavelengths.

In order to improve the flexibility of concen- I rtric cables, a fabricated tubular conductor of woven wire is sometimes employed, but such a construction is not altogether satisfactory at ultra high frequencies on account of the imperfect contact between said wires, which causes In the folby the term ultra high frequency energy is energy at wavelen ths upto about 20 centimetres.

The'object'of the present invention .is to enable ultra high frequency energy to be transmitted along a hollow conductor possessing qualities offlexibility and absence .of mechanical distortion upon bending and which mayserve as I an outer conductor of a concentric'cable, or as a wave guidewithout undue energy losses.

One feature of the present invention consists in the use in a system for the transmission. of

ultrahigh frequencyenergy of a hollow conductorv forming a wave guide orthe. outer conductor of a concentric cable for-the transmission of said energy, said hollow conductorbeing .com-

posed of a'woven orbraided structure of sheath form comprising strands or strips wherein most or all of the individual strands or strips, or collective assemblies of strands or strips, are insulated from each other in order to reduce ultra high frequency energy. losses.

According to another feature. of the invention, 'a. high frequency waveguide for the transmission of ultra high frequency energy consists of a single hollow conductor in the form of .a woven or braided structure composed ofv strands or .strips,=and wherein mostrorall of the individual strands or strips, or collective assemblies of strands or. strips, are insulated fromeach other in. orderto reduce ultra high frequency energy losses, saidwoven or braided structure being supported upon afiexible member of insulating material of low energyloss at ultra high frequencies,

and-which permits the wave guide to be bent Without deleterious deformation of the vcrosssectional form of the guide.

According to a further feature of the-invention, a concentric cable for the transmission of ultra high frequency energy as hereinbefore defined is provided with an outerconductor consisting of a.

woven or braided structure of sheath form composed of :strands or strips, most or all of the strands or. strips or collective assemblies of strands or strips being insulated from each other in order. in operation to reduce energy losses at ultra high frequencies, said outer conductor being supported by a continuous sheath of insulat- .the inner and outerconductor of a concentric .cable of a large :number of relatively small Wires each-insulated from the other in some suitable manner as, foryinstance, by coating the wire withan'insulating enamel, the Wires being braided together. The insulation of the separate wires from each other is said to reduce the skin effect at. high frequencies.

The transmission of television signal frequencies by concentric conductors is referred to in the British patent, but no reference is made to ultra high frequencies. At

. such ultra high frequencies it is found that energy'losses occur mainly as a result of the setting up of local circulating currents between individual braided conductors, unless these conductors are. insulated from each other; and the present invention is therefore not 'concerned'with reduction of thev skin effect, but'with reduction of energy losses due-to local circulating-currents in the braided'conductor or guide.

It is found that by insulating the strands or strips forming. the sheath'conductor, circulating currents therein are eliminated and losses due rto'such currents areprevented. Furthenzby weavingor braiding the insulating-strands to- -ether they may be held suificiently close to prevent-any substantial leakage of flux which would cause losses even when the sheath conductor is flexed.

nrahner known in the art. central conductor may be maintained in spaced In order that the invention may be more clearly understood and readily carried into effect, one form of concentric cable and one form of wave guide, each provided with a sheath conductor according to the invention, will now be described in greater detail by way of example with reference to Figs. 1 and 2 respectively, of the accompanying drawings.

Referring to Fig. 1 of the drawings, the concentric cable there diagrammatically shown, consists of an inner conductor l of drawn copper wire of 18 S. W. G. which is held centrally of a sheath 2 of insulating material (known as polyethylene) by a thread 3 of the same material, and the outer conductor consists of a braided sheath 4 composed of strands of copper wire of 38 S. W. G., the individual strands being insulated from each other by enamelling or shellac. The outer protective covering of the cable consists of a sheath 5 of polyethylene.

Since the cable is especially suitable for u'se at centimetre wavelengths, it is important that the insulating materials employed should be of low loss at such wavelengths. The material polyethylene has been selected for the purposes described as it combines the advantages of good insulating qualities with low energy loss at high frequencies and flexibility, although mechanically strong. Itis also durably resistive to weather conditions.

The inner conductor I of the cable maybe of any suitable form and may be held in spaced reiationship from the sheath 4 in any other suitable For example, the

relationship with respect to the conducting sheath 4 by providing a wrapping of insulating material around the central conductor, the wrapping being composed of any suitable material such as a length of string impregnated with an insulating material wound around the central conductor with a long pitch, in the manner i1- lustrated by the thread of polyethylene 3 in Fig. 1.

While it has been stated that the individual strands composing the conducting sheath 4 are insulated by enamelling or shellac, they may be covered with cotton or other suitable insulating material. The Weaving of the strands is preferably effected so that each strand lies with respect to the central conductor with a long pitch. While as shown the braided sheath is composed of sets of single conductors, individually insulated, a number of conductors may be twisted togather and then insulated as a whole, assemblies of stranded conductors insulated in this manner then being woven to form the conducting sheath.

Although the strands are preferably circular in cross-section, they may, if desired, be in the form of substantially fiat strips or tapes. If desired, two or more conducting sheaths may be provided. one enclosing the other.

Referring to Fig. 2 of the drawings, the wave guide shown consists of a braided conducting sheath 6 which is made in a manner similar to the conducting sheath 4 shown in Fig. 1, but is of larger diameter. The principal mechanical support for the sheath 6 consists of a tube 1 of polyethylene, which is made by winding a strip of this material into tubular form. In order to prevent the sheath 6 from sagging in gaps which may be formed between abutting edges of the wound strip of polyethylene, a layer B of thinner strip polyethylene is wound upon the base 1. .The outer surface of the conducting sheath 6 is protected firstly by a layer 9 of oiled silk or similar material of strip form, and wound upon this again is a substantial protective covering ID of rubber in strip form which is wound to a desired thickness.

The diameter of the conducting sheath 6 will be determined by the frequency and type of the radiation that it is desired to propagate, and also it will depend upon the dielectric constant of the insulating material employed to support the sheath. In a practical construction the external diameter may be 4 centimetres, the sheath 6 being constructed of strands of copper wire of 38 S. W. G. enamelled and closely braided around the supporting tube of polyethylene.

A wave guide of the form shown in Fig. 2 may be flexed without introducing undesirable distortion of the cross-sectional form of the conducting sheath 6, and undesirable eifects which would otherwise occur are therefore avoided. If the tube 7 does not combine mechanical strength with flexibility to the degree'desired to avoid collapse when flexed, measures may be adop'tedto increase the degree of support.

In order to reduce losses which might arise due to the presence of the insulating material, the minimum amount of such material should be employed consistent with the requisite mechanical-strength.

What I claim is:

1. A flexible wave guide for the transmission of ultra high frequency energy comprising a single hollow conductor, said hollow conductor being "composed of a plurality of conductive strands braided and individually insulated from one another in order to reduce ultra high frequency losses, 3, layer of oiled silk surrounding said hollow conductor, and a flexible strip of insulating material of low energy loss at ultra high frequency, said flexible strip being wound into a tubular form and located inside said hollow conductor for supporting it.

2. A flexible wave guide for the transmission of ultra high frequency energy comprising a single hollow conductor, said hollow conductor being composed of a plurality of conductive strands braided and individually insulated from one another in order to reduce ultra high frequency losses, a layer of oiled silk surrounding said hollow conductor, a protective coating of rubber surrounding said layer of oiled silk, and a flexible strip in the form of a strip of insulating material of low energy loss at ultra high frequency, said flexible strip being wound into a tubular form and located inside said hollow conductor for supporting it.

3. A flexible wave guide for the transmission. of ultra high frequency energy comp-rising a single hollow conductor, said hollow conductor being composed of a plurality of conductive strands braided and individually insulated from one another in order to reduce ultra high frequency losses, a layer of oiled silk surrounding said hollow'conductor, and two layers of flexible insulating strips wound into a tubular member forming a continuous sheath of low energy loss at ultra high frequency located inside said hollow conductor for supporting it. a

4. A flexible wave guide for the transmission of ultra high frequency energy comprising a single hollow conductor, said hollow conductor being composed of a plurality of conductive strands braided and individually insulated from one another in order to reduce ultra high. frequency losses, a layer of oiled silk surrounding said hollow conductor, a protective'coating of rubber surrounding said layer of oiled silk, and two layers of flexible insulating strips wound into a tubular member forming a continuous sheath of low energy loss at ultra high frequency located inside said hollow conductor for supporting it.

5. A flexible wave guide for the transmission of ultra high frequencies up to about 20 centimeters, comprising an insulating tube formed by an insulating strip being wound into a tubular form, a second insulating strip wound over said first insulating strip in an opposite direction from the winding of said first strip, a braided conductive sheath, each strand of said conductive sheath being insulated and supported by said insulating tube, a third insulating strip wound over said braided conductive sheath in the same direction as said first mentioned insulating strip, and a rubber strip wound over said third insulating strip in the same direction as said second mentioned insulating strip.

6. A flexible wave guide for the transmission of ultra high frequencies up to about 20 centimeters, comprising an insulating tube formed by a first insulating strip being wound into a tubular form, a second insulating strip which is thinner than said first mentioned insulating strip and wound over said first insulating strip in an opposite direction from the winding of said first strip, a braided conductive sheath of stranded copper wire having an external diameter of about 4 centimeters, each strand of said copper wire being insulated and supported by said insulating tube, a third insulating strip wound over said braided conductive sheath in the same direction as said first mentioned insulating strip, and a rubber strip wound over said third insulating strip in the same direction as said second mentioned insulating strip.

7. A flexible wave guide for the transmission of ultra high frequencies, comprising an insulating tube formed by an insulating strip being wound into a tubular form, a second insulating strip wound over said first insulating strip in an opposite direction from the winding of said first strip, a braided conductive sheath, each strand of said conductive sheath being insulated and supported by said insulating tube, a third insulating strip wound over said braided conductive sheath in the same direction as said first mentioned insulating strip, and a protective strip wound over said third insulating strip in the same direction as said second mentioned insulating strip.

EDWARD CECIL CORK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,781,093 Aifel Nov. 11, 1930 2,034,047 Leibe et a1 Mar. 17, 1936 2,204,737 Swallow et a] June 18, 1940 2,348,752 Quayle May 16, 1944 2,407,690 Southworth Sept. i7, 19%

FOREIGN PATENTS Number Country Date 485,948 Great Britain May 27, 1928 

